4 and 6 October, 2006

Chapter 12

Mechanism of Transcription

Overview• Transcription is superficially similar to replication, with important

differences.• E. coli RNA polymerase core has an ’ subunit structure.• In Eukaryotes, RNA Pol II transcribes most genes.• Transcription consists of initiation, elongation, and termination.• Initiation occurs at promoters, which are recognized by the subunit and

the -CTD in bacteria.• Promoter strength depends on a close match to the consensus sequence.• Promoter binding is followed by a transition to the open complex.• RNA polymerase transition to elongation phase involves abortive initiation.• Termination is mediated by signals in the RNA.• In Eukaryotes, promoters contain binding sites for TFIID, TF2B, and TBP.• Initiation involves a multiprotein assembly at the promoter.• Elongation is stimulated by elongation factors, and involves the recruitment

of capping, splicing, and polyadenylation proteins.• PolI and PolIII promoters are distinct, but require TBP.

Transcription and RNA Polymerases

RNA Polymerase Structure

Events in Transcription

70 Recognizes Bacterial Promoters

Core polymerase binding is enhanced by sigma and increased temperature.

Promoter Consensus

Polymerase Binding

-CTD contacts the UP element.

-CTD contacts the UP element.

RNA Pol Active Site and Channels

RNA Polymerase melts -9 to +3

The subunit contains the active site.

Termination

Termination

Rho

Three Eukaryotic RNA Polymerases

Eukaryotic Promoter

SV40 Early transcription starts at the same position relative to the TATA box.

Subunit Structure of Pol II

PolII Initiation

General Factor Order of Addition

TBP Minor Groove Interactions

TBP Binding

TBP Recruits TFIIB

TFIID is complex

Roles of TFIID Components

Activation by SP1 requires TAFII-110

TFIID interacts with activators.

Binding of TFIIE

Phosphorylation of the Preinitiation Complex

TFIIH Phosphorylates RNA Pol II

TFIIH Helicase Activity

Promoter Clearance

Transcriptional Initiation with Mediator Complex

Mediator

Elongation

Cap Structure

Polyadenylation and

Termination

Pol I Promoter

Pol III Promoter

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